(1) Field of the Invention
The present invention relates to an air-to-fuel ratio control system for an internal combustion engine, and more particularly to a system wherein the air-to-fuel ratio of the mixture can be controlled to the one other than the stoichiometric ratio.
(2) Description of the Prior Art
Closed loop air-to-fuel ratio control systems have been highly appreciated for purifying exhaust gases emitted from internal combustion engines. One of these techniques is disclosed in U.S. Pat. No. 3,910,240. This disclosed technique is available for controlling air-fuel mixture to a richer or leaner mixture than the stoichiometric ratio, but does not suffice for practical use in that engine cylinders must be supplied with the mixture of different air-to-fuel ratios to each other requiring more than two mixture supply sources.